In the past, a gas barrier film in which a thin layer of a metal oxide such as aluminum oxide, magnesium oxide, or silicon oxide is formed on a plastic substrate or on a film surface has been widely used for packaging of a product which requires a barrier for various types of gases such as water vapor and oxygen as well as for packaging to prevent quality change of, for example, foods, industrial products, or medicinal products. Aside from the use for packaging, a gas barrier film is also used as a substrate for a liquid crystal display, solar cell, and organic electroluminescence (EL), for example.
As a method for producing these gas barrier films, there are mainly known the following methods: a method for producing a gas barrier film with plasma CVD (Chemical Vapor Deposition); a method containing the steps of coating a coating liquid containing mainly polysilazane, then, applying a surface treatment thereon; and a method of combining these two methods (for example, refer to Patent documents 1 to 3).
In the invention described in Patent document 1, it is disclosed that the compatibility of thick film formation for high barrier property and inhibition of cracks is achieved by the lamination forming method, which contains a wet method to form a polysilazane film having a thickness of 250 nm or less, followed by irradiating the formed film with vacuum ultraviolet rays at least two times.
However, by the method described in Patent document 1, it was found that there remained a problem of insufficient flexibility when lamination was only repeated to achieve a higher gas barrier property. In addition, there produced a phenomenon in which the cut edge portion of the film was vigorously broken caused by the stress given during the cutting process of the film. The effective area as a final product was decreased due to the crack of the cut edge of the film. It was newly revealed that a problem of decreased production yield was resulted.
In the invention described in Patent document 2, it is disclosed a method in which polysilazane is laminate-coated on the gas barrier layer formed with a vacuum plasma CVD method, then the gas barrier layer is repaired by carrying out heat treatment to further improve the barrier property. However, the performance as a gas barrier layer for an organic photoelectric conversion element was insufficient. Accordingly, a further improved gas barrier property, for example, a moisture permeating rate notably lower than 1×10−2 g/m2·day has been desired. Moreover, since the heat treatment of polysilazane requires the conditions of 160° C. for 1 hour, it produced difficulty of the limited application case to thermal resistive resin substrates.
In the invention described in Patent document 3, it is disclosed a method in which polysilazane is coated on a gas barrier layer formed with a vacuum plasma CVD method to make the film smooth, then, a conductive film is formed. By this method, although the compatibility of high barrier property and surface smoothness can be achieved, the stress during bending is concentrated to the gas barrier layer to result in breakdown of the barrier layer due to the unrelieved stress, and a current status is holding a problem of inferior bending property.